Hi Marc, thank you.
That was my first idea I tried. But the system froze in the moment when two green interfaces became active. The service manager was not accessible. I had to reinstall the whole system.
Best regards, Marko

Sorry to hear your system froze, it worked for me. If you encounter the same problem and want to avoid reinstallation, you can reset the network (as described in the manual, see links posted by @mrmarkuz) as well as changing network configuration from command line:NethServer Community